Robotic platform

ABSTRACT

An articulated vehicle including a main frame, a drive system disposed on the main frame, and at least one arm having a proximal end and a distal end. The proximal end of the at least one arm being pivotally coupled to the main frame and the distal end being pivotable above the surface. The vehicle also including an articulator motor disposed on the main frame and coupled to the at least one arm for pivoting the at least one arm above the surface and about the transverse axis, and a slip clutch coupled between the articulator motor and the at least one front arm for enabling rotation of the at least one front arm without rotation of the articulator drive motor when a torque between the at least one front arm and the main frame exceeds a threshold torque.

CROSS REFERENCE TO RELATED APPLICATIONS

This U.S. patent application is a continuation of and claims priorityunder 35 5 U.S.C. §120 from U.S. patent application Ser. No. 10/745,941,filed on Dec. 24, 2003, now U.S. Pat. No. 7,597,162, which is adivisional of U.S. patent application Ser. No. 10/202,376, filed on Jul.24, 2002, now U.S. Pat. No. 6,668,951, which is a divisional of U.S.patent application Ser. No. 09/888,760, filed on Jun. 25, 2001, now U.S.Pat. No. 6,431,296, which is a divisional of U.S. patent applicationSer. No. 09/237,570, filed on Jan. 26, 1999, now U.S. Pat. No.6,263,989, which claims priority under 35 U.S.C. §119(e) to U.S.Provisional Application 60/096,141, filed Aug. 11, 1998, and U.S.Provisional Application 60/079,701, filed Mar. 27, 1998. The disclosuresof these prior applications are considered part of the disclosure ofthis application and are hereby incorporated herein by reference intheir entireties.

STATEMENT AS TO FEDERALLY SPONSORED RESEARCH

This invention was made in part with Government support under contractDAAL01-97-C-0157 awarded by the Army Research Laboratory of theDepartment of the Army. The Government may have certain rights in theinvention.

BACKGROUND OF THE INVENTION

The invention relates to a robotically controlled mobility platform.

Robots are useful in a variety of civilian, military, and lawenforcement applications. For instance, a robotically controlledmobility platform inspect or search buildings with structural damagecaused by earthquakes, floods, or hurricanes, or inspect buildings oroutdoor sites contaminated with radiation, biological agents such asviruses or bacteria, or chemical spills. The platform can carryappropriate sensor systems for its inspection or search tasks. Militaryapplications include operations that are deemed too dangerous forsoldiers. For instance, the robot can be used to leverage theeffectiveness of a human “pointman.” Law enforcement applicationsinclude reconnaissance, surveillance, bomb disposal and securitypatrols.

The mobility approaches that have been used in prior robotic platformsexhibit various shortcomings, many of which are addressed by the presentinvention.

SUMMARY OF THE INVENTION

In one aspect, in general, the invention is an articulated trackedvehicle. The vehicle has a main section which includes a main frame anda forward section. The main frame has two sides and a front end, andincludes a pair of parallel main tracks. Each main track includes aflexible continuous belt coupled to a corresponding side of the mainframe. The forward section includes an elongated arm having a proximalend and a distal end. The proximal end of the arm is pivotally coupledto the main frame near the forward end of the main frame about atransverse axis that is generally perpendicular to the sides of the mainframe.

Alternative embodiments include one or more of the following features:

The arm is sufficiently long to allow the forward section to extendbelow the main section in at least some degrees of rotation of the arm,and the arm is shorter than the length of the main section.

The center of mass of the main section is located forward of therearmost point reached by the distal end of the arm in its pivotingabout the transverse axis.

The main section is contained within the volume defined by the maintracks and is symmetrical about a horizontal plane, thereby allowinginverted operation of the robot.

The vehicle is dimensioned for climbing a set of stairs. At a firstadjusted angle between the main section and the forward section, theforward section rises more than the rise of the bottom-most of the setof stairs. At a second adjusted angle between the main section and theforward section, the length spanned by the combination of the mainsection and the forward section being greater than the diagonal span oftwo successive stairs. The center of gravity of the vehicle is locatedin a position so that the vehicle remains statically stable as it climbsthe stairs at the second adjusted angle.

The forward section includes a second arm, also pivotally coupled to themain frame near its forward end. For instance, the arms are coupled tothe main frame such that they rotate outside the main tracks. The twoarms can be rigidly coupled and rotated together by the articulatormotor. The articulator motor provides sufficient torque between the mainframe and the arms to raise the rear end of the main section therebysupporting the vehicle on the front section. Continuous rotation of thearms can provide forward locomotion of the vehicle. A harmonic drive canbe coupled between the articulator motor and the two arm. The harmonicdrive provides a torque to the two arms greater than the torque providedto it by the articulator motor. A clutch can be coupled between thearticulator motor and the two arms. The clutch allows rotation of thearms without rotation of the motor if the torque between the arms andthe main section exceeds a limit. A pair of flexible forward tracks canbe coupled to the two arms.

A pair of drive pulleys for supporting and driving each of the main andforward tracks are included, one on each side of the vehicle. The drivepulleys are coaxial with the transverse axis of rotation of the arms,and are joined so that they rotate together. The vehicle can include apair of drive motors, one coupled to both the main and forward drivepulleys on a corresponding side of the vehicle.

On each side of the main frame, two compliant pulleys are coupledbetween one of the main tracks and the main frame, and multiplecompliant track supports are coupled between the tracks and the sideplates. Each pulley includes a compliant outer rim, a hub, and multiplecompliant spoke segments coupled between the rim and the hub.

Multiple compliant longitudinal track supports coupled between the mainframe and the continuous belts. Each longitudinal track support has aseries of open slots forming a series of rib sections between the upperand lower edges of the support.

The pulleys and main frame are recessed within the volumes defined bythe tracks.

Each track includes a flexible continuous belt and a series of compliantcleats attached transversely on the outside of the belt.

The main tracks each include a longitudinal rib coupled to the insidesurface of the belt, and each of the pulleys includes a channel aroundits circumference which accepts the longitudinal rib. The channels aredimensioned larger than the rib thereby allowing debris to be caughtbetween a pulley and a tracks without dislodging the track from thepulley.

In another aspect, in general, the invention is a method for operatingan articulated tracked vehicle having a main tracked chassis and apivoting forward arm for the vehicle to climb a set of stairs. Themethod includes pivoting the arm to raise the arm higher than the riseof the bottom-most stair of the set of stairs, then approaching thefirst stair until the arm contacts the first stair. The method furtherincludes driving the main tracks until the main tracks contacts thefirst stair, and then pivoting the arm to extend the tracked base of thevehicle. The method then includes driving the main tracks to ascend theset of stairs.

In another aspect, in general, the invention is a method for invertingan articulated tracked vehicle which has a main tracked chassis and apivoting arm. The method includes supporting the vehicle on the maintracks in a first vertical orientation, supporting the vehicle on thepivoting arm, and then pivoting the arm to raise the main chassis abovethe supporting surface. Further pivoting of the arm passes the mainchassis past a stable point. This results in the vehicle being supportedon the main tracks in a second vertical orientation, the second verticalorientation being inverted with respect to the first orientation.

Aspects of the invention include one or more of the followingadvantages. One advantage is immediate recovery from tumbles in whichthe vehicle lands on its “back.” The vehicle can operate with eitherside up and therefore does not necessarily require righting. Also, ifone vertical orientation is preferable over another, for example, due toplacement of sensors, the robot can invert itself to attain a preferredorientation.

Another advantage is impact resistance. Impact resistance allows therobot to operate even after collisions, falls, or tumbles. Furthermore,impact resistance allows deploying the robot in a variety of waysincluding tossing it from a height, such as from a window or from ahelicopter.

The housing of components within the track volume has the advantage thatthe robot's components are less likely to be damaged in a fall ortumble. Recessing the side plates of the robot frame within the trackvolume also reduces the likelihood of impacting the frame in such atumble or fall.

The robot's forward center of gravity has the advantage that it aidsstair climbing and climbing of steep inclines. Also, a center of gravitywithin the extent of the forward articulated section allows the robot toperform a self righting operation and to operate in an upright postureby supporting the platform solely on the forward section.

The robot's articulated body, including continuously rotatable arms, hasthe advantage that the robot can be driven using a “paddling” action ofthe arms. This mode of driving the vehicle is useful, for instance, whenthe tracks have inadequate traction, for example due to an obstructionsupporting the center of the frame.

Compliant idler and drive pulleys provide robustness to debris that maybe caught between the tracks and the pulleys. Also, raised segments onthe tracks mating with corresponding channels in the outside rims of theidler and drive pulleys reduces the possibility of “throwing” a track.Loose mating of the raised segments and the channels also permits debrisbeing caught between the pulleys and the track without throwing a trackor stalling a drive motor.

Other features and advantages of the invention will be apparent from thefollowing detailed description, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates teleoperator control of a robot;

FIG. 2 is a functional block diagram of system components of a robot;

FIGS. 3 a-c are a perspective, side, and top view, respectively, of arobot;

FIGS. 4 a-g show idler and drive pulleys;

FIG. 5 is a perspective view of a robot frame;

FIG. 6 is a schematic side view of the stowed position;

FIG. 7 a is a schematic side view of the inclined position;

FIGS. 7 b-c are schematic side views of a maneuver to raise an objectusing the inclined position;

FIGS. 8 a-c are schematic side views of a maneuver to achieve an uprightposition;

FIG. 9 is a schematic front view of the “wheelie” position;

FIGS. 10 a-b are schematic side views of a self-righting maneuver;

FIG. 11 is a schematic view of a stair climbing maneuver;

FIGS. 12 a-c are schematic side views of a maneuver to recover from ahigh centering;

FIG. 13 is a schematic side view illustrating “paddling” using the arms;

FIGS. 14 a-b are schematic views showing camera placement;

FIGS. 15 a-b are schematic views showing placement of sonar sensors;

FIGS. 16 a-b are schematic views showing placement of infra-red sensors;

FIG. 17 is a diagram showing a door opening mechanism.

DETAILED DESCRIPTION

Referring to FIG. 1, a version of the system includes a robot 100, and aremote control system 150. Remote control system 150 allows an operator160 to control robot 100 from a distance. The operator can selectdifferent levels of human control over the robot, ranging from ateleoperation mode, in which the operator directly controls the motorsand actuators on the robot, to autonomous operation, in which theoperator passes higher-level command to the robot. In partiallyautonomous operation, robot 100 can perform tasks such as following awall, recovering from being stuck in an opening or due to high centeringon an obstruction, evading a moving object, or seeking light.

Robot 100 moves around its environment on a pair of parallel main tracks110 and a pair of tapered forward tracks 120. Main tracks 110 aremounted on a main body 140 of the robot. Robot 100 is articulated. Inparticular, forward tracks 120 are mounted on a pair of forward arms130, which are pivotally attached to the main body 140 and can bepositioned at any angle to main body 140. Robot 100 is designed to moveabout in a variety of environments, including an urban environment ofbuildings (including staircases), streets, underground tunnels, andbuilding ruble, as well as in vegetation, such as through grass andaround trees. Robot 100 has a variety of features which provide robustoperation in these environments, including impact resistance, toleranceof debris entrainment, and invertible operability. The robot's design issymmetrical about a horizontal plane so that it looks the same upsidedown and can operate identically in either orientation. Therefore, therobot can recover quickly from a tumble or fall in which it is inverted.

Referring to FIG. 2, robot 100 includes an onboard control system 210,which includes one or more computer processors and associated memorysystems. Onboard control system 210 is coupled to a drive system 220,which includes motors that drive main and forward tracks 110 and 120 anddrive arms 130. Onboard control system 210 is coupled to a communicationsystem 230, which includes, for example, a radio for exchanging controland feedback information with remote control system 150. Robot 100 canoptionally carry a sensor system 240, including, for example, a camera,to provide feedback to operator 160. Sensor system 240 also providesinput to onboard control system 210, such as the angle between arms 130and the main body. These inputs are used during fully or partiallyautonomous operation. Robot 100 can also optionally carry a manipulatorsystem 250, including, for example, a door opening device, for use underremote or autonomous control.

FIGS. 3 a-c show robot 100 in a fully extended configuration in whichforward arms 130 extend beyond the front of main body 140. Thecombination of forward tracks 120 and main tracks 110 and provide anextended length base. Main body 140 includes a vertically symmetricalrigid frame 310 which includes parallel vertical side plates 312. Sideplates 312 are rigidly coupled by tubes 320 and 322 and an articulatorshaft 330. The rigid components are designed for strength and low weightand are made from a material such as 7075-T6 aluminum. Alternativeversions of the robot can use other materials, such as other lightweightmetals, polymers, or composite materials.

Referring to FIGS. 4 a-f, main tracks 110 and front tracks 120 includecompliant belts made of a solid polyurethane or a similar flexiblematerial. The belts are highly abrasion resistant and have high strengthand minimal stretch due to internal steel or fiber cording. Referring toFIGS. 4 a-d, each main track 100 is driven by a toothed main drivepulley 342. Teeth 410 in each main drive pulley 342 mate with grooves412 on the inside surface of the corresponding main track 110. Referringto FIGS. 4 e-f, a smooth surfaced main idler pulley 340 supports eachmain track 110 at the rear of the robot. Both main drive pulleys 342 andmain idler pulleys 340 have V-shaped channels 343 around theircircumference. These grooves loosely mate with an integral offsetV-shaped rib 341 on the inside of each main track 110. The main andfront tracks have soft elastomer cleats 350 spaced along their length.In alternative embodiments, main and front tracks are smoothhigh-friction tracks.

Alternative versions of the robot can use other types of tracks, such astracks made up of discrete elements. However, debris may be caughtbetween elements and such tracks are generally heavier than flexiblebelts. Other flexible materials can also be used for continuous belttracks. Referring back to FIGS. 3 a-c, each front track 120 is narrowerbut otherwise similar to main tracks 110, having grooves and a V-shapedsegment on the inside surface, and soft cleats 350 attached to theoutside surface. A front drive pulley 344 drives each front track 120.Each front drive pulley 344 is toothed and has a central V-shapedchannel that loosely mates with the V-shaped rib on the inside of thecorresponding front track 120. On each side, front drive pulley 344 iscoaxial with main drive pulley 342, and both drive pulleys on aparticular side turn in unison on a common axle. A smaller smoothsurfaced front idler pulley 346, which also has a V-shaped channel,supports each front track 120 at the extreme end of the correspondingarm 130.

Referring again to FIGS. 4 a-f, each of the drive and idler pulleys 340,342, 344, 346 are compliant (75D durometer) and are made of apolyurethane or a similar material. Although flexible, the design andmaterial stiffness provides resistance to lateral loading. Each pulleyhas a series of radial spokes 352 around a central hub 354. Spokes 352support a thin outer rim section 356. The combination of spokes 352 andthin outer ring section 356 provide a compliant support for the trackthat can deform if debris is caught between outer ring section 356 andthe track. This allows debris to be caught without necessarily stallinga drive motor or throwing a track.

Referring to FIG. 4 g, an alternative version of the idler and drivepulleys also has a spoke pattern, but the spokes are “angled” ratherthan being radial. Angled spokes 357 have less tendency to buckle ondirect impact. Alternative materials can also be used, providing more orless compliance, depending on the impact resistance and payload capacityrequirements for the robot.

Referring to FIG. 5, on each side, between drive pulley 342 and idlerpulley 340. Compliant main track supports 314 provide support for maintrack 110. Track supports 314 are made of the same material as the driveand idler pulleys. Main track supports 314 are attached by screws to thetop and bottom surfaces of side plates 312. Each main track support 314has a series of angled slots. The slots in the track supports are formedsuch that a series of angled ribs 315 join the top and bottom edges ofthe tract support. These ribs bend when the top and bottom edges of atrack support are forced together, thereby providing compliant supportfor each track.

Referring back to FIGS. 3 a-b, front tracks 120 are supported by armside plates 332 using front track supports 334. Front track supports 334are wedge-shaped and each has a series of angled slots similar to thosein main track supports 314. The arm side plates 332 on each side of therobot are rigidly coupled to one another through articulator shaft 330,and therefore move together.

Referring to FIG. 3 b, front arms 130 can be continuously rotated aroundarticulator axle 330 as indicated by circle 360. On each side, an armsupport 362 is attached to the side plate 312. When arms 130 are rotatedto a “stowed” position next to the side plates 312, the front idlerpulleys 346 have a clearance fit next to the corresponding arm supports362. Both arm supports 362 and arms 130 have polymer pieces, such asDerlin, on the mating surfaces.

The robot's mobility system is powered by three separate electricalmotors. Referring to FIG. 3 c, on each side of the robot a respectiveidentical drive motor 370 is coupled to main and front drive pulleys 342and 344 by a chain and sprocket mechanism (not shown).

Referring still to FIG. 3 c, an articulator drive motor 372 is used tocontrol the angle between arms 130 and the main body. Articulator drivemotor 372 is coupled to the input of a harmonic drive 374 which providesa gear reduction to articulator axle 330. Harmonic drive 374 has acentral opening through which articulator axle 330 passes. The output ofharmonic drive 374 is coupled to a slip clutch 376 which provides outputtorque to articulator axle 330. Slip clutch screws 378 are tightened toprovide adequate transfer of torque to rotate arms 130 while allowingthe articulator axle to slip in the event that a large torque is appliedto the arms. Articulator axle 330 passes through a central opening indrive pulleys 342 and 344 and is attached to arm side plates 332.

In this version of the robot, drive motors 370 and articulator motor 372are 90 watt DC brushed motors. In other versions of the robot, brushlessmotors can be used. Drive motors 370 are geared down 32.7:1 to the drivepulleys. Harmonic drive 374 provides a 427:1 gear reduction betweenarticulator drive motor 372 and articulator axle 330, thereby providinga maximum torque of approximately 127 N·m to arms 130. Slip clutch 376prevents overloading of harmonic drive 374 if the torque exceeds themaximum torque that can be provided by articulator drive motor 372, forinstance due to an impact on the arms.

Due to the placement of the motor and drive components, the center ofmass of robot 100 is well forward. In particular, referring to FIG. 3 b,center of mass 364 falls within the circle 360 of rotation of arms 130.This location enables or aids certain maneuvers such as stair climbingand self righting, as are described below.

Referring to FIG. 3 c, robot 100 includes a payload volume 370 betweenside plates 312, and between structural tubes 320 and 322. The mainbody, including the payload volume, and the drive motors and drives, ishoused in a thin, impact resistance, polycarbonate shell (not shown).The main body is totally within the volume defined by the main tracks,and furthermore is sufficiently thin to provide ground clearance in bothupright and inverted orientations of the robot.

As an alternative to payload being contained within payload volume 370,payloads can be placed on the top of the robot, preferably near thecenter of mass to aid operations such as stair climbing. Althoughinvertible operation may not be possible in this case, larger payloadscan be carried in this way.

Referring again to FIG. 5, each of the idler pulleys are attached toside plates 312 by a pulley holder 510 which attaches to the side plateusing a series of radially positioned screws 515. Screws 515 passthrough slots 520 in the side plates. This allows each pulley holder toslide in a back and forth direction. A tensioning screw 530 passesthrough a hole in side plate 312 and mates with threads in pulley holder510. Tensioning screw 530 is used to adjust the position of the pulleyholder prior to tightening the screws. Pulley holders 510 include ballbearings 530 which support the idler pulleys. A similar slot andtensioning screw arrangement is used on the front tracks (not shown inFIG. 5). The front and main drive pulleys are attached to side plates314 using similar pulley holders which mate with holes 522 (rather thanslots) in the side plates 312. The tensioning mechanism allows easyreplacement of the tracks, for example, to change a cleat design ormaterial to better match the environment the robot must traverse.

Rather than using ball bearings 530 to support the drive and idlerpulleys, alternative versions of the robot can use small diameterpolymer bearings. Although polymer bearings have somewhat greaterfriction, they cost less than ball bearings and reduce maintenance dueto dirt contamination. Polymer bearings are also more shock resistantthan ball bearings.

This version of robot 100 is sized to be portable, and is approximately62.5 cm (24.6″) long (with arms stowed) by 50.8 cm (20″) wide by 16.8 cm(6.3″) high, and weighs 10.5 kg (23 lbs.) The robot can be carried by aperson on his or her back, for example, attached to a special frame orstowed in a backpack. Structural tube 320 can also serve as a carryinghandle.

Main tracks 110 are 7.6 cm wide (3″) and front tracks 120 are 5.1 cmwide (2″). Cleats 350 extend 0.95 cm (0.4″) from the outside surface ofthe tracks. Approximately half of the frontal area of the robot istracked. Main tracks 110 are wide for maximum “grab” of the surfaceduring normal high speed locomotion and are separated sufficiently forefficient skid steering. Front tracks 120 are as small as possible to beeffective while minimizing the mass of arms 130. In alternative versionsof the robot, the front tracks can be made even narrower since thearticulation is designed for limited use in certain situations, such asstair climbing.

All the main and front drive and idler pulleys are 2.54 cm (1″) wide,thereby minimizing the area that debris can be caught between thepulleys and the tracks, while still being able to deliver maximum powerto the tracks.

Rigid frame 310 and payload volume provide a ground clearance of 4.1 cm(1.6″) on either side. The robot can carry a payload of up to 10 kg (22lbs.). If the payload is positioned over the center of mass, the robotcan still perform operations such as stair climbing.

In operation, robot 100 is designed to maneuver at high speed in roughterrain. It may collide with objects and suffer tumbles and falls. Forinstance, the robot may tumble when descending stairs. Furthermore, therobot may be deployed by tossing it out of a helicopter. Therefore, therobot is designed to be as impact resistant as possible. Also, as therobot is completely invertible, it can immediately continue operationafter it is inverted in a fall or collision.

Impact resistance is accomplished, in part, by surrounding much of thevehicle with compliant main and front tracks 110 and 120 with softcleats 350. The tracks and cleats provide a first layer of impactprotection. The tracks are supported by compliant idler and drivepulleys 340, 342, 344, and 346 and by compliant main and front tracksupports 314 and 334, which, working together, provide a second layer ofimpact protection.

Referring back to FIG. 3 a, side plates 312 are recessed within thetrack volume, thereby reducing the likelihood that the frame will bedirectly impacted from the side in a tumble or a fall. Similarly, themain body and payload volume are recessed relative to the top and bottomof the main tracks, thereby reducing the likelihood that the main bodywill be impacted.

In the event of a tumble or a fall, arms 130 can be vulnerable to damageif they are extended away from the main body. For instance, a falllaterally onto the tip of an arm could damage it. However, arms 130 are,in general, used in situations where the possibility of a fall is small.In most operations, the robot will have the arms “stowed” at its sides.Arm supports 362 provide significant lateral support to the arms duringimpacts in the stowed position. To further prevent possible damage, whenrobot 100 detects that it is in free fall using its sensor system, itautomatically assumes the stowed position without requiring operatorintervention.

Robot 100 is designed to maneuver in dirt and debris. There is apossibility that such dirt and debris can be caught between the tracksand the drive and idler pulleys. The idler and drive pulleys arecompliant and can tolerate material being caught between them and thetracks. The V-shaped ribs 341 (FIG. 4) on the inside surfaces of thetracks which mate with the V-shaped channels 343 on the pulleys are deepenough to prevent “throwing” a track. Also, the fit between the V-shapedchannel and the V-shaped grooves is loose thereby allowing debris to becaught without necessarily dislodging the V-shaped segment. Furthermore,the idler pulleys do not have teeth, thereby further reducing the effectof debris entrainment by allowing debris to pass under the idler pulleysin the grooves of the tracks. Finally, the pulleys are narrow, therebyminimizing the places that debris can be caught.

Further debris resistance can be obtained in alternative versions of therobot using active debris removal approaches. For instance, a stiffbrush positioned before each pulley can prevent debris from entering thepulleys. Compressed air jets can also be used in place of the brushes toremove debris on the tracks. Flexible or rigid skirts, placed at anangle in front of each of the pulleys, can also divert debris before itenters the pulley.

Referring to FIG. 3 c, robot 100 is controlled using left and rightdrive motors 370 and articulator motor 372. Steering is accomplishedusing differential speed of the tracks on either side of the robot. Therobot will, in principle, skid around its center of gravity 364 (shownin FIG. 3 c) allowing complete turning with the extremes of the robotstaying within a 100 cm (39.4″) diameter circle.

In operation, robot 100 has several mobility modes including fullyextended, stowed arms, inclined, upright, and “wheelie” modes. Inaddition, robot 100 can perform several maneuvers including selfrighting, stair climbing, and recovery from high centering.

A fully extended mode is shown in FIGS. 3 a-c. In this mode, the longestpossible “wheelbase” is achieved. This mode is useful, for instance, ina stair-climbing maneuver describe below.

Referring to the schematic view of FIG. 6, the stowed arms mode is themost compact configuration of robot 100. Arms 130 are stowed next to themain track such that both main tracks 110 and forward tracks 120 providetraction. This configuration is used for high speed mobility and fortraversing rough terrain. It is also the configuration that is used whenrobot 100 is launched by tossing or dropping it through a window or dooror when the robot tumbles.

Referring to FIG. 7 a, robot 100 can deploy arms 130 to raise theforward end of the main body in an inclined mobility mode. This postureis useful for increasing ground clearance to traverse rubble-strewnterrain and to increase the height of sensors on the platform, such as aCCD camera. Note that in the inclined mobility mode, the robot travelson four points of contact at the extreme ends of each track, somewhat asit were on wheels instead of tracks.

Referring to FIGS. 7 b-c, by combining the inclined mode with the fullyextended mode, the robot can lift and carry objects, rather like aforklift. Referring to FIG. 7 b, robot 100 first adopts the fullyextended position with its arms 130 outstretched and then maneuvers itsarms under an object 630 to be carried or lifted. Referring to FIG. 7 c,robot 100 then raises itself into the inclined mobility position, thusraising object 630. The object needs to be small enough to fit betweenthe tracks, of course, in order to be carried away by the robot.

Referring to FIGS. 8 a-c, to assume an upright “prairie dog” mode, robot100 balances the main body on arms 130. Referring to FIG. 8 a, robot 100begins in a stowed position, and then using articulator drive motor 372(FIG. 3 c) applies a torque to the arms. Since the center of gravity iswithin arc of the arms (as shown in FIG. 3 b), the main body is raised(FIG. 8 b) until it reaches a high position (FIG. 8 c) which is short ofthe point at which the robot would topple. As is described furtherbelow, this upright position allows sensors to be placed at the highestpossible elevation, and also provides the smallest possible wheel base.In this upright mobility mode, the robot is able to drive on the fronttracks and to pivot in place with the tracks staying within a smallcircle, in principle, as small as 60 cm (23.6″) diameter. Therefore, theupright mobility position is useful for navigating in narrow corridorsand passageways.

Referring to FIG. 9, a side “wheelie” mobility mode is used to navigatea passageway that is even smaller than the width of the robot in theupright position. In the side wheelie mode, the robot rests one track onthe side wall and the other track on the floor. It then moves forward ina tilted orientation as shown.

Referring to FIG. 10 a-b, a self righting maneuver is related to theupright mobility mode. In this maneuver, in order to invert itself, therobot begins in a stowed mode and raises itself as it does whenattaining the upright mobility mode (FIGS. 8 a-c). However, rather thanstopping in the upright position shown in FIG. 10 a rotation iscontinued past the vertical point and the robot falls over (FIG. 10 b),thereby completing the inversion.

Referring to FIG. 11, robot 100 can raise arms 130 in order to mount anobstacle, such as a stair 1010, in its path. To mount the first step ofstaircase 1110, robot 100 raises its arms 130 and drives forward toraise its main tracks 110 onto the first stair. The robot then assumes afully extended mode thereby extending its wheelbase to increase itstability and to provide as smooth a ride a possible up the stairs. Softcleats 350 (not shown in FIG. 11) provide mechanical locking with thestair edge needed to drive the robot up the stairs.

Robot 100 is specifically dimensioned to climb common stairs in thisversion, with step dimensions of up to a 17.8 cm (7″) rise and 27.9 cm(11″) tread. As the robot tilts or inclines, the vertical projection ofthe center of gravity (CG) with respect to the ground moves backwards.For stable travel on stairs, the extended wheel base of the main andforward tracks in the fully extended mode span a minimum of two steps(i.e. at least 66.2 cm (26.1″) for 17.8 cm (7″) by 27.9 cm (11″) stairs)such that the vehicle is supported by at least two stair treads at alltimes. Note that robot 100 can climb larger stairs for which it cannotspan two steps, but the traverse will not be as smooth as the robot willbob with each step.

To avoid nosing up or down (pitch instability) while climbing stairs,the vertical projections of the center of gravity is located in a stablerange which is at least one step span (i.e., 33.1 cm (13″) for 17.8 cm(7″) by 27.9 cm (11″) stairs) in front of the furthest rear main trackground contact and at least one step span behind the front most fronttrack ground contact.

Alternative versions of the robot can use shorter track dimensions thatdo not satisfy the requirement of spanning two steps, and the center ofgravity can be outside the stable range. Although such robots may not beas stable on stairs, inertial effects add to dynamic stability atincreased velocities, smoothing the traverse on stairs. Also, the frontextremities of arms 130 can be weighted to move the center of gravityforward in the fully extended position. However, adding weight at theend of the arms also has the negative effect of reducing robustness.

Referring to FIGS. 12 a-c, robot 100 has relatively small verticalclearance below its main body. In this version of the robot, in order toaccommodate the drive motors and gearing within the front section of themobility platform resulted in only 4.11 cm (1.6″) ground clearance onboth top and bottom of the robot. Referring to FIG. 12 a, robot 100 canlose traction in a high centering situation in which it rests on anobstacle 1110. Referring to FIGS. 12 b-c, arms 130 are lowered(illustrated here as swinging clockwise to the front of the robot) togain traction with the ground and then the robot can drive away in theinclined mobility mode.

Referring to FIG. 13, another mode of recovery from high centering makesuse of continuous rotation of arms 130. Continuous rotation in onedirection essentially “paddles” the robot off obstacle 1210 using onlythe articulator drive motor 370, for example.

Note that the likelihood of a high centering situation is reduced forrobot 100 since approximately half of the frontal area that is tracked.Therefore, obstacles are as likely to encounter the tracks as to passunder the main body.

The robot's low and forward positioned center of gravity also allows therobot to climb steep inclines, given enough traction, without the robottoppling. Based on the location of the center of mass, this version ofthe robot can, in principal, climb a 77° incline.

Robot 100 includes the capability of carrying a variety of sensors,including cameras, sonar sensors, infra-red detectors, inertial sensors,motor position, velocity and torque sensors, inclinometers, a magneticcompass, and microphones. Sensors can be placed on all surfaces of therobot.

Sensors can be shielded within the track volume or within the protectiveshell of the main body. The front and rear of the vehicle has room forsensors within the 24.4 cm (10″) width not covered by tracks, althoughthe rear is partially occluded by the rear handle. The top and bottom ofpayload volume 370 (FIG. 3 c) is free for sensor placement, as are sideplates 312. Sensors mounted to the front of arm supports 362 areoccluded when arms 130 are stowed. Sensors can also be mounted on armside plates 332. Articulator axle 330 is hollow allowing power andsignal cables from the arms to pass to a slip ring allowing continuousrotation of the arms. The robot's self-righting capability permits theuse of fewer specialty sensors since not all sensors have to beduplicated on both the top and the bottom of the main body. When thereis redundancy of sensors on both the top and bottom of the robot, thisfeature allows the robot to continue functioning if one or more of itssensors fails—it simply inverts and uses the undamaged sensors on theother side.

Referring to FIGS. 14 a-b, a two- or three-camera array 1310, which isused for stereoscopic vision, is placed at the top of the robot foroperation predominantly in the upright mobility position only (FIG. 14b). Another camera 1320 is placed at the front of the robot fornavigation and video transmission back to remote control system 150.Camera array 1310 and camera 1320 have fields of view 1315 and 1325respectively. A microphone (not shown) is placed at the front forsurveillance and for providing directional information. A rate gyroscopeis placed near the center of gravity 364 of the robot. Optionalaccelerometers can be located near the rate gyroscope.

Referring to FIGS. 15 a-b, two sonar sensors 1420 are placed at the topand bottom of the robot respectively, for operation in the uprightposition (FIG. 15 b). Two more sonar sensors 1410 are placed on thesides of the robot to be as high as possible when the robot is in theupright position. The sonar sensors are positioned high off the groundbecause they have a fairly large cone of sensitivity, and may beconfused by the ground or very small objects if placed low to theground.

Referring to FIGS. 16 a-b, four infrared sensors 1530 are placed at thefront of the robot, and two on each side 1510 and 1520, one in the backand one in the front. The side-back IR's are in the same position as theside sonar sensors and can be used in either upright or stowed position,while the side-front infra-red sensors 1520 are occluded by the arms instowed position and are only used in upright position.

In this version of the robot, there are no rear-facing sensors, althoughthey can be added if needed. Robot 100 can move to its upright mobilityposition to use the sonar sensor on the bottom of the robot. Or, it canrotate quickly in either the stowed position or the upright position,which has a very small turn radius, to use its entire sensor suite toacquire information about the environment in any direction.

In addition to placing sensors directly on the outside surface of therobot, a retractable sensor mast can be extended away from the top orthe bottom of the robot. Sensors, such as cameras, can be mounted on thesensor mast. Robot 100 can include a variety of manipulators. Referringto FIG. 17, one such manipulator is a door opening mechanism that allowsrobot 100 to open a closed door with a standard height door knob 1620.An extendable mast 1630 is attached to the robot. Mast 1630 has a highfriction, flexible hoop 1640 at the top of the mast. Hoop 1640 isrotated by an actuator located within the attachment section of the hoopand mast. The procedure for engaging door knob 1620 is reminiscent of aring toss game. The object is to place the hoop, which remains attachedto the mast, over the door knob. Once the hoop is over the door knob,the mast retracts to snug the hoop against the door knob. The hoop isthen rotated and the door knob is rotated due to the frictional forcesholding the hoop against the door knob. Once the door has been jarredopened, the mast extends to disengage the hoop from the doorknob.

Alternative versions of the robot can be completely waterproofed,thereby allowing underwater operation. Also, larger or smaller versionsof the robot can be used for different applications. The drive system inother versions of the robot can allow independent rotation of the arm oneach side of the robot, and separate drive motors for the main and fronttracks can be used.

Remote control system 150 (FIG. 1) provides a user interface to operator160 that allows teleoperation of robot 100.

Alternative versions of the remote control system 150 supportteleoperation as well as a means of switching between teleoperation andautonomous control. The user interface permits transitions betweenautonomous and teleoperated control that are almost imperceptible to theuser. That is, the user can interrupt autonomous operation of the robotat any time to give commands and direction, and the robot would operateautonomously when not receiving particular directions from the user. Thesystem provides a predetermined warning signals to the operator, forinstance if it is unable to operate autonomously, possibly by means of avibrating unit that could be worn by the operator and which would beeffective in a noisy environment. In addition, the user can addadditional tasks to the robot's mission and request notification fromthe robot when milestone tasks have been achieved.

Versions of the robot can perform various autonomous tasks which can beinitiated by the operator from remote control system 150. These includeobstacle avoidance, wall following, climbing stairs, recovery from highcentering, returning “home,” opening doors, searching for a designatedobject, and mapping. The robot can use the various mobility modesdescribed above in these autonomous operations, and if necessary, cancall for operator assistance during its execution of a task. Alternativeconfigurations of articulated bodies can be used. For example, a singlecentral “arm” can be used and the arm or arms do not necessarily have tobe tracked.

Other embodiments of the invention are within the scope of the followingclaims.

What is claimed is:
 1. A method performed by an articulated vehicle, themethod comprising: driving the articulated vehicle along a drivedirection over a surface, the vehicle comprising: a main frame havingright and left sides; a drive system disposed on the main frame andconfigured to maneuver the articulated vehicle over the surface, thedrive system including a pair of parallel main tracks each coupled to acorresponding side of the main frame and each being driven by acorresponding drive pulley rotating about a transverse axis generallyperpendicular to the sides of the main frame and between a top of theparallel main tracks and a bottom of the parallel main tracks; at leastone arm having a proximal end and a distal end, the proximal end of theat least one arm being pivotally coupled to the main frame about thetransverse axis that the drive pulleys rotate about; an articulatormotor disposed on the main frame and coupled to the at least one arm forpivoting the at least one arm above the surface and about the transverseaxis; and a sensor system; detecting, using the sensor system, that thearticulated vehicle is in free fall; and in response to detecting thatthe articulated vehicle is in free fall, automatically and withoutoperator intervention assuming a stowed position by rotating the atleast one arm, using the articulator motor, so that the at least one armis next to the parallel main tracks.
 2. The method of claim 1, whereindriving the articulated vehicle along a drive direction comprisesnegotiating a set of stairs.
 3. The method of claim 1, wherein the robotcomprises an additional arm pivotally coupled to the main frame aboutthe transverse axis that the drive pulleys rotate about, and whereinassuming the stowed position comprises rotating the additional arm sothat the additional arm is next to the parallel main tracks.
 4. Themethod of claim 3, wherein each of the at least one arm and theadditional arm comprises a compliant track including a compliant beltmade of a flexible material and a plurality of elastomer cleatslongitudinally spaced along an outer surface of the compliant belt, sothat the tracks provide a layer of impact protection to an onboardcontrol system of the articulated vehicle.
 5. The method of claim 2,wherein negotiating a set of stairs comprises negotiating at least onestair of the set of stairs having a rise of at least 7 inches (17.8 cm)and a tread of at least 11 inches (27.9 cm).
 6. The method of claim 1,wherein driving the articulated vehicle along a drive directioncomprises traversing debris.
 7. The method of claim 1, wherein thesensor system comprises one or more of: inertial sensors, velocity andtorque sensors, and inclinometers.
 8. The method of claim 1, whereineach of the drive pulleys is a compliant pulley intervening between oneof the parallel main tracks and the main frame to provide a layer ofimpact protection to an onboard control system on the main frame.
 9. Themethod of claim 8, wherein the onboard control system is enclosed withina volume of the parallel main tracks, and wherein each compliant pulleyis formed of a compliant polymer.
 10. The method of claim 8, comprising,after landing from the free fall, inverting the articulated vehicleusing the at least one arm.
 11. The method of claim 10, whereininverting the articulated vehicle comprises: supporting the vehicle onthe parallel main tracks on a supporting surface in a first verticalorientation; supporting the vehicle on the at least one arm; andpivoting the at least one arm to raise the main frame above thesupporting surface.
 12. The method of claim 11, wherein inverting thearticulated vehicle comprises: further pivoting the at least one armpast a stable point, resulting in the articulated vehicle beingsupported on the parallel main tracks in a second vertical orientation,the second vertical orientation being inverted with respect to the firstvertical orientation.